Telephone system



May 18, 1937.

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ATTORNEY.

May 18, 1937.

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ATTORNEY.

Patented May 18, 193'? UNITED STATES TELEPHONE SYSTEM John Wicks, Oak Park, Ill., assignor to Automatic Electric Company, Limited, Liverpool, England,

a British company Application May 13, 1935, Serial No. 21,199

22 Claims.

The present invention relates to telephone systems. It is concerned particularly with telephone systems in which the interconnection between lines is effected through the operation of automatic switching apparatus. The object of the invention is to produce a new and improved telephone system in which the amount of equipment withheld from common use by reason of a conversational connection having been set up between a pair of lines is at a minimum.

General description In carrying out the general object of the invention, and in applying the invention to automatic telephone systems, two separate trains of switches are provided, one to be used exclusively for the setting up of connections from a calling line to a desired line, while the other train includes switches positioned under the control of the switches in the first-named train and through which the conversational connections are established. It will be understood, therefore, that the invention is applied to the improvement of what is known as separate-setting and speaking-route systems. One feature of the invention resides in the arrangement whereby the setting switches (or the by-pass switches, as they are sometimes called) are maintained entirely separate from the conversational switches with no fixed relationship as to the relative numbers, while at certain switching stages temporary interconnection between setting and conversational switches is provided by means of what are referred to as tie switches. Through the interconnection temporarily effected by means of the tie switches, the conversational switches are positioned according to the position taken up by the setting switches, the positioning of the conversational switches being, in general, accomplished by a hunting movement to hunt for a conversational switch in a group marked according to the positioning of the by-pass or setting switches.

A feature of the disclosure is that all of the conversational switches, including those used for the purely non-numerical or preselection stage,

are of the same rotary type of switch mechanism, each having access to one-hundred outlets.

A further feature is that the switches in the by-pass train which respond to setting impulses are of the Strowger vertical and rotary type, while the switches in the conversational train are of the rotary or single-motion type,

A further feature resides in the arrangement for providinga common group of finder distributors for a number of 100-line groups of finders.

A further feature of the disclosure is that a by-pass final selector has access to five 100-line groups of subscribers lines, being controlled by the preceding hundreds by-pass selector to determine to which of the five 100-line groups the connection is to be extended.

A further feature is concerned with the provision of a group-common conductor at each of a plurality of switching stages for controlling the hunting operation of the tie switches hereinbefore referred to. All of the conversational switches which have access to the same group of outlets or trunks are considered as a group. A group-common conductor is assigned to the group of switches. A multiple of this conductor appears in each of the trunks accessible to the group of switches, as well as in each of the outlets from the tie switches to a conversational switch of the group, and is useful in directing the tie switches so that connection is made thereby to a conversational switch having access to a trunk line over which the desired conversational connection may be completed, or to direct the operation of the tie switch so that it makes connection with the trunk line to which a predetermined conversational switch has access. I

The invention also includes a number of additional features of novelty in a system such as briefly outlined above, as will appear more fully hereinafter.

Description of drawings Referring now to the accompanying drawings, comprising Figs. 1 to 12, they show by means of the usual circuit diagrams a sufficient amount of the equipment in a telephone system embodying the invention to enable the invention to be understood. More in particular, Figs. 1 to 6 show switching apparatus through which a connection maybe set up from the line of substation A, Fig. l, to the line of substation B, Fig. 6; Figs. 7 to .12 show common controlling or by-pass equipment forming a train of setting or by-pass switches which are taken into use temporarily while a connection is being established, but which forms no part of the established talking connection; and Fig. 13 (on the same sheet as Fig. 3) shows an overflow circuit to which an attempted connection may be routed in the event that an all-trunks-busy condition at a given switching stage precludes the completion of the connection to the desired line.

In the conversational train, two non-numerical switching stages are provided, represented respectively by the primary finder PF, Fig. l, and

the secondary finder SF, Fig. 2; three numerical or selecting switching stages are provided, represented by the thousands selector TS, Fig. 3, the hundreds selector or pre-final selector PS, Fig. 5, and the connector or final selector FS, Fig. 6. When the usual decimal system is followed, the three numerical switching stages afford an ultimate capacity of ten thousand lines.

Each of the single-motion rotary switches of Figs. 1 to 6 is assumed to have fifty contacts in the bank of each wiper, as is indicated by the numeral (53) located adjacent each of the abovenamed switches. By the expedient of providing a duplicate set of wipers, as shown, the capacity of each switch is increased to one hundred outlets.

The grouping of the conversational switches, and the arrangement of the switches in the bypass train will now be considered.

From the standpoint of the by-pass train of switches, the originated calls are distributed by distributors such as DS, a group of whichis assigned to five lOO-line groups of subscriber lines in the present disclosure. Each distributor is provided with a tie-switch such as the tie switch TSI, each of which has access to fifty primary finders, such as the primary finder PF, Fig. 1. It is assumed that ten primary finders suffice to serve a one-hundred line sub-group, and that fifty finders, therefore, serve five 100-line groups, all accessible from one fifty-outlet switch, such as the tie switch TSi, Fig. '7.

As many distributors as may be required are assigned to the 500-line group above discussed, one additional distributor being indicated, the distributor DS', having the tie switch TSI. The banks of the several tie switches of the same group are suitably multipled together, as is indicated by the inter-bracket line MB.

In common with the other distributors associated with the same 500-line group, and with distributors atiother 500-line groups, the distributor DS has access to twenty-five by-pass thousands selectors, of which the by-pass thousands selector PTS, Fig. 9, is one. Accordingly, each of the semi-circles of bank contacts associated with wipers of the distributor DS contains twenty-five contacts, as indicated by the numeral (25) placed above the switch. This number, of course, is somewhat arbitrary, as a larger number or smaller number may be used in practice.

In common with other by-pass thousands selectors, the by-pass thousands selector BTS, Fig. 9, (having ten levels of bank contacts) may have access to ten groups of lay-pass pre-final selectors, of which the by-pass pre-final selector BPS, Fig. 11, is one.

For the purpose of testing called lines and guiding final selectors (such as the final selector FS, Fig. 6) into association with desired called lines by-pass final selectors (such as the by-pass final selector BFS, Fig. 12) are provided, each of which has access to the terminals of the lines in five loll-line groups. Accordingly, the same by-pass final selector may be reached over five levels of the by-pass pre-final selectors. The terminals shown in association with the wipers l 14-! l 18 of the bypass pre-final selector BPS, Fig. 11, are assumed to be the first terminals in levels I to 5. It is to be noted that, as regards the terminals accessible to wipers EH5, Hi6, and [8, the terminals of the five levels indicated are multipled together and are connected to conductors H31, H36, and l I30, extending to the by-pass final selector BFS. The second terminals in the same levels may be similarly multipled together and connected to the second by-pass final selector, and so on. With this arrangement, the same by-pass final selector may be seized responsive to a dialled digit which directs the by-pass pre-final selector to any one of five levels. In order, therefore, that the bypass final selector shall be able to distinguish between five one-hundred line groups to which it has access, the contacts accessible to the line-test wiper ill? of the by-pass pre-final selector BPS are not multipled together, but each extends to a separate wiper of the by-pass final selector BFS, whereby the hundred-line group with whicheifective connection is made is determined. by the level over which the by-pass final selector BFS is seized. The fifth to tenth levels of the by-pass pre-final selector BPS are similarly associated with another 500-line group, by way of another group of by-pass final selectors.

The function of the non-numerical stage tie switch TSI, Fig. 7, having been described generally, attention will now be directed to the firststage and second-stage tie switches TS2 and TS3, Figs. 8 and 10. The tie switch TS2, Fig. 8 has access to a maximum of fifty finder-selector links, such as the link interconnecting the secondary finder SF, Fig. 2, with the thousands selector TS, Fig. 3. When the by-pass thousands selector BTS, Fig. 9, is seized (over conductors Ml-M5 by a distributor such as the distributor DS, Fig. 7), the tie switch TS2 is caused to operate to select an idle link of which the secondary finder, such as the finder SF, has access to the primary finder (such as the primary finder PF,) taken for use by the tie switch TSI. Thereafter, the circuits of Fig. '7 and Fig. 8 cooperate to cause the secondary finder to hunt for and connect with the primary finder used to find the calling line, whereby the conversational path from the calling line is set up through a primary finder and a secondary finder as far as a thousands selector, such as the thousands selector TS, Fig. 3.

When the by-pass pre-final selector BPS, Fig. 11, is seized (by way of conductors 93l-935 by a by-pass thousands selector, such as the selector BPS, Fig. 9), the tie switch TS3 is caused to select a trunk line extending to a pre-final selector (such as the selector TS, Fig. 5) which is accessible to the particular thousands selector, such as TS, taken for use by the preceding tie switch, such as TSZ. Thereafter, the circuits of Figs. 8 and 10 cooperate to position the thousands selector on the trunk selected by the tie switch TS3, whereby the conversational path from the calling line is extended as far as a pre-final selector, such as the selector PS, Fig. 5.

Subsequently, a level-common conductor, such as the fifth-level-common conductor H38, is marked by the positioning of the by-pass pre-final selector BPS, and the seized pre-final selector PS is controlled from the circuits of Fig. 10 to select a final selector in the group indicated by the level to which the by-pass pre-final selector BPS has been operated.

Subsequently, the seized by-pass final selector (such as the by-pass final selector BFS, Fig. 12) is operated to make connection with the called line and to enable it to be tested to ascertain its busy or idle condition, following which the, selected final selector, such as the final selector FS, Fig. 6, is caused to complete the conversational connection to the line (if idle) under the control of the circuits of Fig. 10, in cooperation with the circuits of Fig. 4, and as determined by the positioning of the by-pass pre-final selector and the by-pass final selector (such as BPS, Fig. 11 and BFS, Fig. 12).

As will be subsequently explained in detail: (1) the connection set up to a by-pass thousands selector, such as BPS, Fig. 9, through a distributor such as is indicated in Fig. 7 is released as soon as the conversational connection has been completed to a thousands selector, such as TS, under the control of the non-numerical-stage and firststage tie switches, whereafter the connection between the calling line and the by-pass thousands selector is maintained through a tie switch such as the tie switch TSZ; (2) as soon as the connection has been further extended by a thousands selector (such as TS, Fig. 3), to a pre-final selector (such as FS, Fig. 5), the Icy-pass thousands selector (such as BPS, Fig. 9), and associated tie switch are released, and the connection to the by-pass pre-final selector (such as BPS) from the calling line is maintained through a tie switch, such as T83; and (3) as soon as the connection has been completed to the desired line (through a pre-final selector such as PS, Fig. 5), and a final selector (such as FS, Fig. 6), the connection from the calling line to the by-pass pre-final selector (such as BPS, Fig. 7, by way of a tie switch such as TS3) is released, and the by-pass pre-final selector, together with the by-pass final selector, is released and restored to common use.

From the general description given above of the operation of the system, it may be seen that a first-stage tie-switch, Fig. 8, in testing the finder-selector links to which it has access, must not only find an idle link, but must find an idle link of which the secondary finder such as SF has access to the same primary link to which connection has been made by the non-numerical tie switch, Fig. '7, as it would be futile to select an idle link in a group that does not have access to the primary finders in the calling group. In order to enable this group test to be made, a group-common conductor 25!! is assigned to the group of secondary finders in which the secondary finder SF is located. All of these secondary finders have their banks connected in multiple in the regular way, and the outlets of this multiple of contacts are connected in the regular way through the distributing frame to primary finders in desired hundred-line groups. The groupcommon conductor 260 is multipled to contacts on the right-hand side of the distributing frame DFI, so that an individual conductor, such as I24, of each of the primary trunks accessible to the secondary finders of the group is connected to the group-common conductor 200.

At the other end thereof, the group-common conductor 200 is multipled to various sets of contacts at the upper side of the distributing frame DF4, so that each of the points of access from a tie switch to a secondary finder such as SF includes a conductor such as 235 connected with the group-common conductor 290. In ac cordance with the well known practice of keeping the trunks accessible to a given switch diversified, a tie switch such as TS2 may have access to secondary finders .in a number of the groups, as outlined above, and in testing over its bank the tie switch may encounter trunks of several groups, and may successively test several group-common conductors such as 200. These group-common conductors, however, are all maintained separate from each other and no tie from one group-common conductor to another exists, whereby the group test may be accurately made in amanner which will be described in detai hereinafter.

Similarly, a separate group-common conductor (such as 300) is assigned to each group of thousands selectors (such as TS) to direct the hunting operation at the second-stage tie switches.

Each of the several distributing frames, DFI to DFIU, shown throughout the drawings, may consist merely of suitably mounted blocks of termi nals, together with inter-terminal jumper rings as needed. Bank terminal wires are secured to the terminal of certain of said terminal blocks, while conductors extending to the next order ofswitches are secured to the terminals of other of the terminal blocks, while jumpers are run between the blocks as desired to effect desired interconnections of bank terminal conductors with trunk conductors.

At this point it may be mentioned that the switches are ordinarily mounted in groups of ten 1 or twenty and that the banksof ten switches are ordinarily permanently multipled together by What is known as a bank multiple, and one set of bank wires is extended from one switch of the ten to a terminal block. The group of ten may be further multipled with one or more other groups of ten if desired, and the entire large" group thus formed is suitably connected to trunk conductors, as is well known to those skilled in the art. purpose of making it clear that the various distributing frames indicated are those ordinarily used in automatic exchanges for the purpose of enabling the bank terminals and the trunk terminals to be suitably connected together in the de-. sired manner, and also to make it plain that these distributing frames are not peculiar to the novel system disclosed herein. 1

Detailed description The disclosure having been described generally, a detailed description of the operation of the apparatus shown will now be given. For this purpose it will be assumed first that the subscriber at substation A, Fig. 1, desires to converse with the subscriber at substation B, Fig. 6.

When the receiver is removed at substation 'A, line relay I04 of the individual line circuit LC energizes over conductors IGI and through contacts of cut-01f relay I05. Upon operating, relay lM disconnects the test conductor I03 of the called multiple from the test conductor of thecalling multiple and connects it to ground, so as to indicate a busy condition of the calling line; at its lower armature it connects the resistor ID! in parallel with the winding of cut-off relay I05 so as to indicate the line as calling, in"

the banks of the finders, such as PF, having ac cess to the calling line; and at' its middle armature it places ground potential, from contacts of cut-off relay I05, on start conductor I20, assigned tothe -line group containing the calling, line.

Starting a distributor and a tie switch armature it connects group-mark conductor 14-6" to group-common conductor 15L assignedjto the associated IOU-line group. Conductor I5! is in terconnected' at distributing frame DF l with conductor I31 associated with the primary finder PF, Fig. 1 and with each of, the corresponding:

This brief explanation is given for, the

H32 and" conductors (not shown) associated with the other finders in the sanre 100-line group.

Start relay I08 of the distributor DS energizes through contacts of line-test relay I09 responsive to the ground potential on conductor 141. More-- over, the start relay in each other idle distributor associated with the SOD-line group operates at the same time. Upon energizing, relay I08 at its upper armature closes a driving circuit for the self-interrupting drive magnet I20 of the non-numerical tie switch 'ISI, while at its lower armature it closes a driving circuit through contacts of line-test relay I09 and the selector-test relay III for the self-interrupting drive magnet I30 of the distributor DS. As a result, driving magnet I20 of the tie switch TSI, operating in a buzzer-like manner, advances the wipers 12l- I29 step by step over the contact bank in search of an idle link in the calling IOU-line group, and the driving magnet I30 of the distributor DS operates to advance the wipers l3I-I35 in search of an idle by-pass thousands selector. The search for an idle by-pass thousands selector by the distributor DS is carried out under the control of selector-test relay III, while the search for an idle primary finder link is carried out under the joint control of group-test relay I01 and link-test relay IIO.

At its inner lower armature, start relay I08 energizes the polarizing windings of the electro-- polarized test relay I09, H0, and II I. None of these relays operates responsive to the energize-- tlon of its polarizing winding, as it is so constructed as to require an energization also of its: test Winding, shown in each case as the upper winding of the relay.

Distributor seizes an idle lay-pass thousands selector It will be assumed that the by-pass thousands selector BPS, Fig. 9, is the first one found'to be idle by the distributor DS. That being the base, when wipers I3I-I35 arrive on the contacts from which conductors MI-I45 extend, test wiper I33 encounters a negative potential on conductor I43 by way of the contacts of make-busy key 8I2, armature 843 of relay 804 and its resting contact, conductor 853, off-normal contacts 001 of the selector BPS, and the upper winding of series relay 903. The encountering of this potential by test wiper 133 of the distributor DS results: in the closure of an effective circuit through contacts of clear-out relay H2, contacts of linetest relay 901, the test winding of selector-test relay III, and the middle lower armature of start relay I08 to ground. Selector-test relay III immediately operates over this circuit and. opens the driving circuit of magnet I30 at its lower armature, thereby stopping the wipers of the distributor in engagement with the idle by pass thousands selector BPS, it connects the transfer wiper I35 to the lower winding of trans-- fer relay II3, it immediately marks the by-pass thousands selector BPS engaged by shunting its test winding, thereby applying ground potential directly to test wiper I33; and at its upper armature it connects negative wiper I3I with positivewiper I32 through contacts of line test relay I09, thereby eflecting an immediate energization of line relay I of the by-pass thousands selector BPS with the results to be described hereinafter Tie switch seizes a primary finder As the wipers I2I-I29 of the tie switch TSI' are driven over their contact banks by driving;

magnet I20, group-test wiper I2I successively connects the upper terminal of group test relay I01 to conductors such as I3I, but this is without effect until wiper I2! engages a contact associated with a link assigned to the calling IOU-line group, the link extending to the primary finder PF, for example. When Wiper IZI reaches the terminal to which conductor I3! is connected, a circuit exists for group-test relay I07 from the right-hand terminal of the secondary winding of the transformer I06 (individual to the distributor DS) through test relay I01, group-test wiper 'I2I, and conductor I3I to group-common conductor I5I, and thence by way of contacts of the start relay MI and group-test conductor I46 to the left-hand terminal of the secondary winding of transformer I06. Group-test relay I0I, together with other similar test relays throughout the disclosure, is of the shaded-pole type of alternating current relay, the shaded pole preventing chattering of the contacts in the wellknown manner. Upon operating, relay I01 extends a ground potential from the inner-lower contacts of the energized start relay 708 to the test winding of link-test relay H0, and thence to link-test wiper I20. Assuming that the link extending to the primary finder PF is idle, the test winding of link-test relay H0 is energized over conductor I36, through contacts of switching relay II9 of the primary finder PF, make-busy key I34, and resistor H8. Upon operating, link-test relay H0 immediately shunts its test winding so as to apply ground potential directly to conductor I36 and thereby mark the link engaged and it opens the driving circuit of magnet I20 I of the tie switch TS! so as to stop the Wipers I2I-I29 in engagement with the terminals of the link extending to the primary find-er PF.

As soon as link-busy relay I I0 and selector test relay III are both operated, indicating that the switches TSI and DS are both positioned, a test circuit is prepared for the upper winding of linetest relay I09, and a driving circuit for the seized primary finder PF is closed through contacts of relays I09, H0, and III by way of drive wiper I22. Since the primary finder PF is the one that has been selected, wiper I22 is standing on the terminal of conductor I32, and the circuit extends to self-interrupting driving magnet III of the finder PF. Accordingly, magnet I I7 starts to drive the wipers III-I IS in search of the calling line. At the same time, ground potential is applied to the right-hand terminal of the test winding of line-test relay I09 through contacts of relays H0 and TI I, enabling line-test relay I09 to test the lines as to their calling or non-calling condition, through line-test wiper I23, test conductor I33, and test wipers H3 and [I6 of the finder PF.

Primary finder seizes the calling line When the wipers of the primary finder PF arrive on the terminals of the calling line, test wiper I I3 completes a test circuit for line-test relay I09, Fig. "I, through contacts of cut-off relay I05, contacts of the energized line relay I04, and resistor I01. It is to be noted that the line-test trelay I09 will not operate through a cut-oil relay which is not shunted by a resistor such as I0I.

Upon operating, line-test relay I09 opens the driving circuit of the primary finder PF, and shunts its test winding at its inner upper armature so as to mark the calling line engaged in the :finder (or calling) multiple. Cut-oil relay I05 removes ground potential from start conductor I20; disconnects resistor I01 and substitutes meter I06, and it disconnects ground potential and the line relay I04 from conductors I02 and I M. Y

In the distributor, line-test relay "I09 also connects the positive and negative wipers I24 and 125, through the corresponding wipers I32 and BI of the distributor, to conductors I42 and MI of the by-pass thousands selector BPS, at the same time removing the preliminary energizing bridge previously closed through the upper con-- tacts of selector test relay II I. The line relay 90I of the by-pass thousands selector BPS is henceforth held energized over the calling line through Wipers H2 and ill of the primary finder PF.

Line-test relay 109 of the distributor also opens a point in a special locking circuit for the upper winding of transfer relay H3 at its lower armature, and at its inner lower armature it disconnects start relay 108 from the associated conductor I41 and extends it through contacts of clear-out relay H2 to test wiper 133, at the same time disconnecting wiper 733 from the ground potential previously applied to the test wiper through contacts of selector test relay III and the middle lower armature of start relay I08. The continued energization of start relay I08 is therefore dependent on ground potential applied to test conductor 143 by way of make-busy key 8I2, contacts of relays 804 and 808, conductor 853, and contacts of the now-energized release relay of the selector BPS. It is to be noted that the winding of start relay I08 is shunted by a resistor. This shunt circuit around the winding of relay I08 has a slight tendency to make the relay slow releasing, so as to prevent a restora: tion of the relay while its circuit is being trans ferred from conductor I41 to test wiper I33.

Start relay IOI, assigned to the 100-line group containing the line of substation A, now deenergizes responsive to the above-mentioned operation of cut-off relay I05, unless there is another calling line in the same lOO-line group. At this time, conductor I41, common to fivestart relays ml-I05, becomes ungrounded unless there is an unfound calling line in one of the five IOU-line groups associated with distributor DS. Keeping in mind, that each idle distributor in the group containing the distributor DS is started into operation responsive to the starting ground potential on conductor Ml, it will be appreciated that all other distributors may stop operating and clear out responsive to the removal of ground potential from conductor I47 when relay 'IOI restores.

Result of seizure of lay-pass thousands selector BPS When the by-pass thousands selector BPS is seized as pointed out, and line relay 90I has energized over conductors 85! and 852, release relay 902 is operated by the line relay through contacts of the electro-polarized switching relay 904. At its lower armature, release relay 92 opens a point in the circuit of release magnet 9I2 and prepares a circuit for vertical magnet 9I9; at its inner upper armature it applies ground potential to the polarizing winding of switching relay 904; it applies ground potential to start conductor 855 tostart the associated tie switch TSZ into operation; it places ground potential on conductor 853 so as to provide a holding circuit for the seizing distributor DS; and it connects the test winding of switching relay 994 to the test wiper 923.

As a result of the ground potential on conductor 853,the upper winding of series relay 903 is energized through oif normal contacts 901. Relay 903 thereupon operates and disconnects rotary magnet 9 at its inner lower armature; closes a further point in the vertical-magnet circuit at its lower armature; and at its upper armature it disconnects ground potential from the lower winding of line relay 90I and substitutes ground potential through over-flow con tacts 909 and the secondary winding of dial-tone transformer 95L Accordingly, the calling subscriber is given a dial-tone signal to indicate that he may now begin to dial the digits of the desired number.

Starting the first-stage tie' switch When ground potential is applied to start conductor 855 by release relay 902, a circuit is closed for pulse relay 80I through armature 844 and the inner upper armature of link-test relay 803. Pulse relay 80I thereupon operates in series with drive magnet 820, and closes a direct circuit for the magnet, thereupon magnet 820 operates and opens the circuit'of pulse relay 80L Relay 80I thereupon restores and opens the circuit of driving magnet 820, permitting drive magnet 820 to restore and again close a circuit for the pulse relay. This interaction between the pulse relay and the drive magnet continues until link-test relay 803 operates through contacts of group test relay 807 and link test wiper 826, upon the encountering of an idle link associated with a secondary finder having access to the primary finder used to complete the connection to the calling line.

As the wipers 82I-830 are rotated over the contacts by the above action of drive magnet 820, group test wiper 825 connects group-test relay 801 successively to group-test conductors such as 235, but this is without result until the tie switch TSI has become positioned as pointed out, and relay H0 has operated. After relay H0 operates, each time wiper 825 encounters a link in the group (containing the finder SD) predetermined by the selection of the primary finder PF, a circuit is closed over a conductor such as 235 for the group-test relay 801 and group test relay 801 thereupon responds to connect linktest relay 803 to link-test wiper 326. The source of current for operating group-test relay 805 is the secondary Winding of the transformer 8 (individual to the circuit illustrated), to which the relay is connected through the inner lower armatures of switching relay 805 and stop relay 804. The other terminal of the secondary winding of the individual transformer 8| I is now connected through the middle lower armature and resting contact of switching relay 805, conductor I44, marking Wiper 134 of the distributor DS, contacts of the energized test relays H0 and II I, contacts of transfer relay H3, group-mark wiper I29, and conductor I24, to the group-common conductor 200, assigned to the secondary finder group including the secondary finder SF. This secondary finder group has been definitely marked by the position of the group-mark wiper I29 of the tie switch TSI, as conductors I39 and I24 lead only 'to the group-common conductor 7 200. It will be understood, of course, that other primary finders may have their conductors such as I44 interconnected with other secondary finder groups and therefore with otherv group-common conductors instead of to conductor 200.

With group-test relay 801 operated over groupcommon conductor 200 as above explained, the link-test relay 803 is connected to link test wiper 828 and is thereby permitted to test the links passed over which belong to the secondary finder group to which the group-common conductor 200 is assigned.

seizing an idle secondary finder, SF

It will be assumed for convenience that the link including the secondary finder SF is the first link of the pre-selected group found to be idle, in which case the rotation of the wipers of the tie switch TS2 continues until the terminals of this link are reached, whereupon link-test wiper 820 encounters conductor 236 on which a battery potential is placed by way of resistor 2I0, makebusy contacts 209, and contacts of switching relay 208. Link-test relay 802 now energizes and terminates the hunting operation of the switch. Relay 803 also prepares a circuit for stop relay 804, but this circuit does not become immediately effective, as it is maintained open at the inner lower armature of clear-out relay 808, which relay is maintained operated at the lower contacts of pulse relay I throughout the hunting operation.

A moment after the hunting operation has been terminated by the energization of link-test relay 803, the slow releasing relay 808 restores and completes the energizing circuit of stop relay 804. Relay 804 thereupon closes a locking circuit for itself at its preliminary-make contacts 845; it opens a further point in the hunting circuit at armature 844, as well as its own initial circuit; at armature 843 it breaks one: point in the interconnection between conductors 853 and 854, 1eaving these conductors connected together through the inner upper cont-acts of the now-restored clear-out relay 808; at armature 842 it applies direct ground potential, by way of wiper 826, to conductor 286 so as to guard the link against further seizure; and at armature 842 it prepares a drive and link-test circuit under the control of drive relay 802. At its inner lower armature, stop relay 804 disconnects group-test, relay 801 and substitutes line test relay 806, while at its lower armature it connects up drive relay 802 for a purpose to be explained more fully hereinafter.

Preventing false seizure At this point, it may be pointed out that the above-mentioned clear-out relay 808 is energized during the hunting operation of the tie switch TSZ to maintain the circuit of stop relay 804 opened momentarily after link-test relay 803 has operated so as to prevent a possible false operation which otherwise might occur as follows: assuming that the test for an idle link starts with the wipers of the tie switch standing on one of the last few links of the group and that they are all busy, group-test relay 801 operates but link test relay 803 cannot operate over any of the test conductors of the busy links in the group, but in the event that the first link of the next following group is idle there is a possibility that link test relay 803 may operate before group test relay 807 has had time to restore. With the circuit of relay 804 maintained opened for a slight interval by clear-out relay 808, a spurious operation of relay 803 such as above pointed out results merely in a momentary cessation of the driving movement, as this movement is resumed as soon as group-test relay 80'. restores and opens the circuit of link-test relay 803 and permits it to restore. This operation occurs before the 5100(- releasing clear-out relay 808 has had time to'fall back responsive to the temporary cessation of the operation of pulse relay 80I'.

Operating the secondary finder SF When drive relay 802 is connected up at the lower contacts of stop relay 804 as above pointed out, drive relay 802 energizes over conductor I45, transfer wiper 131, and contacts of relays HI and H2, in series with the lower winding of transfer relay H3 of the distributor DS. Transfer relay 'II3 disconnects mark-wiper 134 from group-mark wiper 129 and transfers it to lineinark wiper I28, preparatory to positioning the seized secondary finder SF on the particular primary finder (PF) through which connection was extended to the calling line.

Preparatory to clearing out the distributor, transfer relay H3 connects its lower winding directly to transfer wiper I35 at its inner lower armature; closes a new holding circuit for the start relay I08 at its middle upper armature, while at its inner upper armature it closes a circuit for the slow-releasing clear-out relay H2. Relay H2 thereupon operates and prepares to release start relay I04 when transfer relay H3 restores. Transfer relay H3 also closes a point in a special locking circuit for itself at its lower armature, so as to prevent a restoration of the transfer relay and the clearing out of the circuit prior to the operation of the line-test relay I09 responsive to the primary finder PF finding the calling line.

In the tie-switch T82, when drive relay 802 operates in series with transfer relay H3, it closes a circuit which includes the actuated armature 84I, armature 848, contacts of line-test relay 806, drive wiper 82I, and conductor 23I, for drive magnet 20'! of the secondary finder SF. The self-interrupting drive magnet 20? now operates to drive the wipers 20I-206 of the secondary finder until line-test relay 808 is energized through line-test wiper 822, conductor 232, and test wiper 203 or test wiper 206, upon the primary finder in use being located.

seizing the primary finder PF In the assumed example, the primary finder in use is the primary PF, accessible to the wipers 20I-203 of the secondary finder SF. When the wipers 20I-203 arrive on the terminals to which conductors IZI-I23 are connected, line test relay 806 energizes through test wiper 203 and over conductor I23, the circuit including contacts of switching relay I I9 of the primary finder PF, conductor I38, line-mark wiper 128, contacts of transfer relay H3, contacts of relays III and H0, mark-wiper I34, conductor 144, contacts of switching relay 805, secondary winding of the individual transformer 8| I, contacts of switching relay 805, and the inner lower armature of the operated stop relay 804.

Upon operating, line-test relay 800 opens the above-mentioned driving circuit of magnet 201 of the secondary finder SF at its upper contact, thereby terminating the hunting operation of the secondary finder, while at its inner upper armature it closes a circuit for switching relay 805. When relay 805 operates, it looks itself at armature 849 to start conductor 855; it opens an additional point in the secondary-finder driving circuit at armature 848; it connects the negative and positive conductors of the secondary finder to the corresponding conductors of the by-pass thousands selector at armatures 84B and 841; at its inner lower and middle lower armatures it transfers the secondary winding of the individual testing transformer 8II into association with the first numerical stage; and at'its lower armature it opens the circuit of drive relay 802 and transfer relay 7 I5. Relay 802 thereupon restores and opens a further point in the driving circuit, at the same time applying ground potential from armature 8M to line test wiper 822, thereby grounding the test wipers 203 and 296 through lead 232. The ground potential on test wiper 203 is extended to conductor I23 to serve as a holding potential as soon as switching relay H9 becomes operated.

Switching-through the primary finder and clearing-out the distributor In the distributor DS, the opening of the circuit of the lower winding of transfer relay H3 at the lower contacts of relay 865, Fig. 8, results in the immediate deenergization of transfer relay II 3, unless the operation of tie switch T82 and of the secondary finder SF have taken place before the primary finder PF has found the calling line. In either event when transfer relay H3 does restore it opens the circuit of slow-acting relay H2 and closes a circuit through contacts of relay I I2, and conductor I31, for switching relay II9 of the primary finder PF. When relay I I9 operates it looks itself to the test lead, now grounded by way of conductor I33 at its inner upper armature; and at its three remainingarmatures it joins the wipers of the finder to trunk conductors I2I, I22, and I23, at the same time disconnecting the line marking conductor I38 from conductor I23.

Transfer relay II3 also opens the circuit of start relay I08 for the length of time required for clear-out relay M2 to restore after its circuit is opened by the transfer H3. Relay I08 therefore restores and opens the circuit of the polarizing and holding windings of relays I29, H I3, and II I, whereupon these three relays restore also. Line-test relay I09 disconnects the positive and negative wipers I24 and I25, thereby opening the connection initially established between the calling line and the by-pass thousands selector PBS; line-test relay I52 also again connects start relay I68 to conductor I41 to enable the distributor DS to be again started into operation pursuant to the handling of a further call. Clear-out relay IIZ falls back a moment after start relay I08 restores.

The calling line is now connected with the bypass thousands selector BPS through the wipers I H, II 2 of the primary finder PF, contacts of switching relay H9, wipers 2M and 202 of the secondary finder SF, wipers 824 and 823 of the tie switch T82, and armatures .846 and 84! of switching relay 865. Switching relay II9 is now held energized over conductor I23 through wipers 203 and 822 by the ground potential placed on wiper 822 through contacts of the restored drive relay 802, and armature 842 of stop relay 804.

From the foregoing description, it will be seen that the distributor DS and the tie switch TSI cooperate to connect the calling line very quickly with an idle by-pass thousands selector through a primary finder and that a secondary finder is subsequently operated to take over the connection formed through the tie switch TSI and the distributor DS. Ihis arrangement serves the twofold purpose of giving the calling subscriber quick access to a by-pass thousands selector so that he may begin sooner to dial the number, and of greatly simplifying the primary and secondary finders at the expense of a somewhat more complicated construction at the distributor and at the tie switch TSZ, which, however, are provided in much smaller numbers than the primary and secondary finders.

Dialling the thousands digit 1 When the calling subscriber, upon hearing the dial tone produced by a dial-tone current transmitted back to his line from the dial tone transformer 95!, as above pointed out, dials the first digit in the desired number, line relay SDI of the by-pass selector BPS is momentarily deenergized a number of times depending upon the value of the digit. Each time it deenergizes, line relay 935 completes a circuit through the lower armatures of the operated release and series relays 9ii2'and 963 for vertical magnet SIIl. By the operation of magnet 9I0, the wipers 92I-925 are raised step by step until they come to rest opposite the desired level ofbank contacts.

The lower winding of series relay 993 is energized in series with vertical magnet H0. Being provided with a conducting sleeve, as indicated, relay 903 is slow-releasing and therefore remains operated throughout the series of impulses.

When the wipers of the switch leave their normal position, off normal contacts 995 prepare a circuit for release magnet 9I2; ofi normal contacts Q05 prepare a circuit for rotary magnet 9| I; and off normal contacts 901 open the initial circuit of series relay 923, leaving the continued operated condition of relay 903 under the control of the lower winding of the relay and the conductive sleeve thereof.

At the end of the digit, relay 92.3 restores, as no further impulses are received. Upon restoring, relay 993 removes the dial tone connection from the lower winding of the line relay SiH at its upper armature and-substitutes the initial direct ground potential; at its lower armature it disconnects vertical magnet em; and at its inner lower armature it connects up the self-interrupting rotary magnet 9 II. Magnet 9| I now operates through off-normal contacts 995 to drive the wipers 92I-925 until the rotary-magnet circuit is opened at the inner lower armature of the electro-polarized switching relay 904.

seizing the lay-pass pre-final selector BPS In the assumed example, the line desired is the line of substation B, Fig. 6. the number of which is assumed to be 1513. Therefore, the first digit dialled being the digit 1, and the wipers of the selector BPS are brought to rest opposite the first level of bank contacts. The contacts shown are assumed to be the'first set of contacts of the first level, being the ones from which conductors 93I-935 extend to the by-pass prefinal selector PBS, Fig. 11. Assuming that the selector BPS is idle when the wipers 92I-925 are rotated onto the first set of bank contacts in the first level. the test Wiper 923 encounters a battery potential over conductor 933, through contacts of make-busy key III9, off normal contacts I I08, and the upper winding of series relay HM. Test wiper 923 being connected through the upper contacts of release relay 902 to one terminal of the test winding of switching relay 9%, the test winding is energized over conductor 854, contacts of clear-out relay 808, conductor 7 circuit of release relay 902 at its inner lower armature; it makes an additional ground. connection to start conductor 855; at its inner upper armature it closes the locking circuit for its polarizing and holding winding to conductor 854; it applies ground directly from the grounded conductor 853 to test wiper 923 so as to mark the seized selector PBS engaged; and it connects up wipers 92L 922, and 925, at the same time disconnecting line relay 90!.

Line relay 90I thereupon restores, and release relay 902 restores a short time later, but without any particular effect at this time, as prior to the restoration of the slow releasing relay 902 ground potential has been returned over conductor 933 from the selector BPS in a manner to be pointed out later. This ground potential is extended through contacts oi relay 904 to conductor providing a holding circuit through contacts of clear-out relay 008 and over conductor 854 for the lower winding of relay 904, now locked to conductor ass at the inner upper contacts of the relay.

In the by-pass pre-final selector BPS, Fig. 11,

; when line relay H02 energizes over the calling line and over conductors 93I and 932, it closes a circuit for release relay H03. Release relay H03 thereupon operates and places ground potential at its middle upper armature, through contacts of make-busy key I I I9, on conductor 933 to provide the above-discussed holding circuit for the by-pass thousands selector BPS. At its upper armature, release relay II03 connects up test wiper IIB; it energizes the polarizing winding of switching relay II05 at its inner upper armature; at its lower armature it prepares an impulsing circuit for vertical magnet IIII; and at its inner lower armature it places a ground potential on start conductor III9.

The by-pass pre-final selector is thereby prepared for operation in response to the second digit in the desired number and the start con ductor III9 is now grounded to start the second stage tie switch TS3 into operation.

At this point it may be well to call attention to the fact that the by-pass pre-final selector BPS is one of a number of similar by-pass selectors provided in extending calls to lines in the first 1000-line group and that the tie switch TS3, individual to the by-pass selector BPS, is started into operation to take a conversational pre-final selector, such as the selector PS, in the first 1000- line group for use pursuant to the positioning of the previously seized thousands selector TS.

Starting the second-stage tie switch TS3 When start conductor III9 is grounded, by relay II03, a circuit is extended through contacts of switching relay I001, and through contacts of link test relay I002, to the pulse relay IOI associated with the drive magnet I020 of the tie switch TS3. Pulse relay IBM and drive magnet I020 interact as described in connection with the corresponding relay and magnet, 80I and 820, Fig. 8, and magnet I020 drives the wipers I02I-I030 in search of an idle selector in the associated #1 thousands group.

In testing for a pre-final selector, the tie switch TS3 tests for a selector which can be reached from the group including the thousands selector TS. All of the selectors in this group have access to the same trunks, and these trunks, of course, are divided more or less equally amongst the various 1000-1ine groups. The group-common conductor 300 is assigned to the group of thousands selectors in which the thousands selector TS is included, and this group-common conductor is therefore connected at the distributing frame DF5 to each of the conductors such as 239 associated with a link through which a tie switch such as TS2 obtains access to a thousands selector of the group. Similarly, group-common conductor 300 is connected at the distributing frame DF2 to a conductor such as 334 of each of the conversational trunks accessible to the group of thousands selectors. It will be understood that group-common conductor 300 is one of several group-common conductors at the first stage, for there is a separate group-common conductor for each group of thousands conversational switches.

The group-common conductor 200 has been marked at the tie switch T82 by group-mark wiper 829 by way of conductor 239. The tie switch TS3, by means of the group-test relay I005 tests for the group-common conductor marked by the tie switch TS2.

seizing and marking the pre-final selector PS When a trunk line accessible to the marked group of switches is reached, group-test relay I005 operates and at its upper contacts connects the link-test relay I002 to the link-test wiper I005 to enable the individual links to be tested as to their busy or idle condition.

Assuming that the trunk line comprising conductors 43I-440, assigned to the pre-final selector PS, Fig. 5, is the first idle one of the links accessible to the marked group, this trunk line is taken for use and the wipers I02I-I030 are stopped on the conductors 43I-440. This operation includes an energization of relay I005 over the marked group-common conductor and the subsequent operation of link-test relay I002.

Group-test relay I005 is connected at this time to the group-common conductor 300 by way of conductor 334 of the trunk comprising conductor 33I-334, a jumper on the distributing frame DFB, conductor 43I, and wiper I02I. The other terminal of group-test relay I005 is connected through conductor 934, group-test and line-mark wiper 924 of selector BTS, contacts of switching relay 904, conductor 856, and contacts of switching relay 805, to the left-hand terminal of the secondary winding of individual transformer 8| I. The other terminal of this secondary winding is now connected through contacts of the operated switching relay 805, contacts of transfer relay 8I0, group-mark wiper 829, and conductor 349 to the group-common conductor 300. Over these circuit connections, group-test relay I005 operates to connect link-test relay I 002 through linktest wiper I025, conductor 435, contacts of makebusy key 4| I, contacts of transfer relay 408, and resistor M2, to the ungrounded pole of the exchange battery.

Upon operating over this path, link-test relay I002 opens the driving circuit and prepares a circuit from start conductor II I9 through contacts of slow-acting series relay I003 for switching relay I001.

A moment later, slow-releasing series relay I003, which is held operated throughout a series of operations of pulse relay IO0I, restores and completes the circuit of switching relay I 001, whereupon relay I007 closes a locking circuit for itself at its preliminary-makeinner upper armature to the grounded start conductor III9; it places ground potential directly on link test wiper I025 to protect the link from further seiz- 

